Citing an individual familiar with the company’s plans, Blass says Microsoft will announce and begin the rollout tomorrow. However, the specific legacy and in-market Lumia and Microsoft-branded Windows Phone devices set to get the update won’t be revealed until tomorrow.

The source also corroborated Blass’s earlier report, which said that Windows Phone users will need to tell their device to manually initiate the update; it won’t be pushed as an automatic over-the-air update.